Warnings: NOT a happy piece.
Notes: This is an idea I've had kicking around for a long time, adapted to its current state after HBP. Many thanks as always to chaoticvanity for the beta. Concrit welcome.
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1.
It was nearly finished - Mandrake grown in blood and sperm, picked before dawn, bathed in milk and honey in the cauldron. Dumbledore collected the dark instruments of life, ready to infuse a spark of being into the lifeless thing.
The creature was just as he had planned – ugly. Its yellow skin formed a more horrid contrast with its black eyes, shriveled complexion and straight black lips. It would be the perfect spy – young, angry, and seemingly corruptible, yet always under his control.
He cast the final incantation. It woke, reaching out its hands.
"Attend. Your name is Severus Snape..."
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2.
Dumbledore had not had to fake his rage after the night Sirius led his creation to the Shrieking Shack.
"Mr. Black, you are an utter disgrace!"
When the students had gone and only the homunculus remained, he sighed and breathed deeply. Perhaps some good would come of this. The creature was undamaged, and now it would have an excuse to study the Dark Arts, to take up with those Dumbledore suspected.
"Go to Lucius and ask him to help you get revenge," he instructed, turning back to his work.
"Fa—" it began, then stopped, jerking itself from the room.
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3.
The creature had slipped out from under his control. It had overheard the beginning of the prophecy and, without consulting him, told Voldemort. Had the Dark Lord discovered his secret – that the spy was not only disloyal but inhuman? More importantly, had Voldemort taken control of the enchantment somehow? Across the table from Dumbledore's weary body, the creature sat, its face twisted into a horrible toothy grimace. Dumbledore tightened his grip on the spell and its face fell blank. He sighed. Not Voldemort, then. Just the magic getting away from him. The damage done, he vowed to be more attentive.
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4.
Dumbledore wept. All his plans, his safeguards, and still he could not save them. They had been beautiful and innocent, and now they were dead. His spy had brought the news, and the child.
"He is not dead," it said flatly, baring the faded skull mark. "The connection remains."
Dumbledore nodded, looking down at Harry, whose sweet face was now scarred by the harsh curse.
"This is my command," he said, speaking ritual words to bind the creature. "Protect him and maintain cover. Nothing else matters."
He stroked the child's hair tenderly. When he looked up, the creature had gone.
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5.
He watched with pride as young Harry was sorted into Gryffindor. The boy had a look of wonder on his face and Dumbledore smiled indulgently.
He glanced over at his spy, checking the strength of his control. Now, more than ever, it was important to have safeguards around the child. The creature scowled as Dumbledore twisted the enchantment, reinforcing his commands.
Another sorting, and a burgeoning friendship formed between Harry and Ronald Weasley. Dumbledore idly imagined Harry's future. He hoped Harry would look up to him, like a grandfather. He wished he'd been able to have children of his own.
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6.
The creature stormed into his office, reverting to its characteristic blankness once they were alone.
"The boy remains incapable of learning Occlumency," it said flatly. "I have terminated the lessons as you allowed."
Dumbledore frowned. Keeping his distance from the boy he loved was taking its toll on the headmaster. He'd have thought the boy a natural. But since the creature's information was always accurate, he knew he would simply have to minimize the damage. He nodded.
The creature scowled again. Dumbledore sighed – the enchantment was taking continuously more power. He waved it away, and the creature grimaced, storming out.
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7.
Young Malfoy was lowering his wand, and Dumbledore thought that he had finally gotten through to the boy, showed him that he could be something other than a follower and a killer. Even ill and surrounded by Death Eaters, he felt hope. Then his spy arrived, and hope blossomed. The creature would dispatch the others; Draco would be saved; Harry would win the day. But as Dumbledore's blue eyes met the creature's black ones, he found himself, for the first time, hearing Severus' thoughts. Severus, a false construction, who shouldn't have had any thoughts.
Now is my chance, he heard. Now is my chance to live.
"Severus," he whispered, beginning to understand almost against his will.
I have drained you, old man; taken your life for my own.
Now Dumbledore knew why he had been so tired recently. He cursed himself for not preparing for this possibility.
You created me, and still you do not know me. You, my father! You did not like to burden the beautiful and innocent with the darkness, so you fashioned an ugly thing to bear that selfsame burden. Ugliness has defined me. You made me, a wretch desperate for love and sympathy, and provided me only misery and vice. Is there no justice here? I have done everything you asked, and still I am an abortion, miserable and abandoned, to be spurned at, and kicked, and trampled on. You gave your love to a Potter, and never to me. No longer.
"Severus… please…" Dumbledore pleaded, becoming aware of the enormity of his own cruelty. He tried to project a determination to make up for his wrongs, but Snape was having none of it.
Goodbye, Father.
As the green light rushed towards him, Dumbledore could only project his final thought. Forgive me, my son.